A wide variety of substances have been proposed for use as fat substitutes in food compositions. The chemical structures of such substances are selected such that they are more resistant to breakdown by the metabolic process of the human digestive system which normally occur upon ingestion of conventional triglyceride lipids. Because of their increased resistance to digestion and absorption, the number of calories per gram available from the fat substitutes is considerably reduced as compared to common vegetable oils, animal fats, and other lipids. The use of such substances thus enables the preparation of reduced calorie food compositions useful in the control of body weight.
U.S. Pat. No. 4,861,613 (incorporated herein by reference in its entirety) describes one class of particularly useful fat substitutes wherein a polyol such as glycerin is alkoxylated with an epoxide such as propylene oxide and then esterified with any of a number of fatty acids or fatty acid derivatives to form an esterified alkoxylated polyol. These substances have the physical and organoleptic properties of conventional triglyceride lipids, yet are significantly lower in available calories than edible oils owing to their pronounced resistance towards absorption and pancreatic lipase enzymatic hydrolysis. The thermal and oxidative stability of the esterified alkoxylated polyols renders them especially suitable for use in the preparation of reduced calorie food compositions requiring exposure to high temperatures such as fried or baked foods.
Various methods of preparing fatty acid-esterified alkoxylated polyols suitable for use as fat substitutes have been proposed, including, for example, the procedures described in U.S. Pat. No. 4,983,329 (direct esterification of propoxylated glycerin using free fatty acids) and U.S. Pat. No. 5,175,323 (transesterification of propoxylated glycerin using alkyl esters of fatty acids). Although such procedures work well, there still exists a need for improved processes wherein manufacturing costs may be substantially reduced or the formation of undesirable impurities or by-products may be minimized. In particular, since polyoxyalkylenes and fatty substances such as triglycerides, fatty acid esters or free fatty acids will undergo thermal and/or oxidative degradation under extreme conditions, it would be highly desirable to develop fatty acidesterified alkoxylated polyol processes which avoid the use of high reaction temperatures for prolonged periods of time.